perf(react-compiler): enable React Compiler for CounterLabel and Truncate

[joshblack]

Follow up to #8505. No issue to close.

This PR enables React Compiler for the first low-risk migration batch, stacked on chore/update-babel-v8-2. All seven files already pass the current compiler check, so no component refactors are needed.

The batch contains 12 changed lines (5 additions and 7 deletions), below the 500-line limit. This is the first review checkpoint; the remaining migrations are not included.

Changelog

New

None.

Changed

• Enable compiler output for CounterLabel/CounterLabel.tsx, Truncate/Truncate.tsx, and internal/components/Caret.tsx.
• Enable compilation of ActionList/ActionList.examples.stories.tsx and stories/deprecated/ActionList.stories.tsx.
• Enable compilation of NavList/NavList.features.stories.tsx and NavList/NavList.test.tsx.
• Add a minor changeset for the published component optimizations. Existing changesets from the base branch remain unchanged.

Removed

Remove these seven files from the compiler exclusion list. No public APIs are removed.

Rollout strategy

• No changes needed in github/github-ui
• Needs changes in github/github-ui
• Ships with feature flag(s)
• Not sure
• None

Minor release: compiler migrations are coordinated rendering changes, without public API or intended visual changes. Use minor changesets for subsequent compiler migration batches, keeping each batch separate and below 500 changed lines.

Testing & Reviewing

• npm run lint:react-compiler -w @primer/react: passed for 840 enabled files.
• npm test -- --run packages/react/src/CounterLabel/CounterLabel.test.tsx packages/react/src/Truncate/Truncate.test.tsx packages/react/src/NavList/NavList.test.tsx packages/react/src/__tests__/storybook.test.tsx: passed (4 files, 383 tests).
• npm run build: passed.
• npm run type-check: passed.
• npm test -- --run: passed (159 files, 2,706 tests; 3 skipped and 10 todo).
• npm run lint: passed.
• npm run lint:css: passed.
• npm run format: passed.
• npm run format:diff: passed.

Direct Oxc checks confirmed all seven files are enabled and have no compiler diagnostics; normal-mode transforms emit memo-cache output for CounterLabel, Truncate, and Caret.

Started Storybook with npm start and used its index.json to select the affected stories. Playwright Chromium smoke checks rendered all 48 selected stories without uncaught page errors or Storybook error UI. Deprecated ActionList stories emit DOM-prop warnings. The temporary Storybook server was stopped afterward.

No new snapshots or visual baselines were added. Dedicated VRT/AVT and github-ui integration were not run (there are no intended visual or accessibility changes).

For review, focus on CounterLabel's accessible count, Truncate's polymorphic props and styles, and NavList's navigation behavior with compilation enabled.

[changeset-bot]

🦋 Changeset detected

Latest commit: 35f5c66

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@primer/react	Minor

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

⚠️ Action required

👋 Hi, this pull request contains changes to the source code that github/github-ui depends on. If you are GitHub staff, test these changes with github/github-ui using the integration workflow. Check the integration testing docs for step-by-step instructions. Or, apply the integration-tests: skipped manually label to skip these checks.

[primer-integration]

Integration test results from github/github-ui PR:

  Changes Waiting
  CI Passed
  VRT Passed
  Projects Passed

[Copilot]

🟢 Approval recommended

The bounded compiler opt-in and release metadata have no identified blocking issues, and reported validation covers the affected behavior.

0 open findings

What changed in this PR

Enables the first small React Compiler migration batch following the Babel 8 tooling update, without component refactors or public API changes.

Changes:

• Removes compiler exclusions for three runtime components and four story/test files.
• Adds a minor @primer/react changeset for rendering optimizations.

File	Description
packages/​react/​script/​react-compiler.mjs	Enables compilation for seven previously excluded files.
.changeset/​react-compiler-low-risk-batch-1.md	Records the component optimizations for a minor release.

🧠 Review effort: Balanced

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